kencombs

All that I've seen in the last 65 years of working on engines (yeah, I'm that old) have been printed, not stamped, on the back side.  Sometimes a base P/N followed by a - and numeric undersize print.  Sometimes just the undersize.   I have no idea what the print material is but it stands up to hot oil.

I use Kirker epoxy, primer, base, clear or single stage paints.   Not quite the coverage of the big boys but w a y cheaper.   Looks good enough for me.
 
That's current use, but I've done different in the past when we had a local 'wholesale paint' store.  Now that they're gone, only the parts houses have paint stuff locally so mine is all purchased online.
 
the only time I really worry about staying with the same brand is base and clear.   Otherwise I've seen no issues with changing brands after the primer.

The engine moves when running and driving.   The rubber protects the steel from work hardening and cracking.

clean it well, really well then spray with auto trans fluid, the bright red stuff.  Now clean again and dust with corn starch.   If's a crack it will show as a red line in the white corn starch.   Cheap guys dye penetrant inspection.   Easier to do on horizontal surfaces, but might work on the side of the block.
 
Or search for 'dye pentrant kit' online.  Lots of them out there, some that even include a black light and the fluids that glow. 
 
Much cheaper and easier than MagnaFlux and works well on cast iron cracks as well as aluminum and other metals

To echo and maybe clarify, compression and flares do not seal on the threads so no sealant needed.  NPT seals on the thread so use sealant if needed.   But, judiciously so that none is allowed to enter the fittings opening.   I try not to have any on the first one or two threads.  

30mph is a very low speed for a driveshaft vibration, at least in my experience.    To help isolate it I'd try these things.
 
1. put the rear end on stands so that it is supported by the springs, not hanging.
   Remove the rear wheels.
   Run the car in gear up to and past 30 and see what you feel.
   Any vibration would point to the driveshaft, but not necessarily balance.   Bad ujoints, a ball and trunion whose trunion is not centered, or even just dry joints can cause it.
 
If not vibration at this point put the wheels on and repeat. 
 
If that doesn't reveal and issue, see if you can find a front end shop with one of the old on the car balancers.  They will reveal exactly which corner is causing the shake.
Slightly bent wheel, tires out of round or otherwise distorted, brake drum out of round etc will all show up with that test.

I would suggest a new coil, just because.   If you're using points, a coil from a Mopar of 12v vintage along with a resistor and start bypass wiring would be best.  Yes, one can get a coil designed to run on 12v, and no they don't have an internal resister (with very few exceptions from the 50s) but are wound with wire that provides the desired resistance.   But, if you do that the starting voltage will be lower than a coil intended to be used with a resistor.  The resistor goes in the switch to coil feed wire.
 
Edit to add:   I'll change my recommendation for coil and resistor.  Use 50/60s GM as they are more readily available and work fine.  And back in the day I saw many more Mopar resistors fail than other brands.  Don't know why, just my experience.

These and the famous Ford 8 and 9 inch are much superior, IMHO, to the 'modern' ones.  At least from a mechanics perspective as adjusting bearings is a snap compared to case spreaders and shims on the 'modern' versions.  Also, setting up gear depth and backlash is a bench job, not an under the car process.   I knew a lot of guys back in the day that had a weekend center section and a weekday version.   4.11s or 4.56s at the strip and 3.08 or 3.23 for the highway.   Most could swap in 30-40 minutes.
 
More common repair for me was axle bearings.  No draining lube to pull the axles.  4 bolts, pop it out, press bearing done. 
 
 
 
 

Carb model would help, some push some pull.    A pic would help too.

We owned a business building that was built in 1917.  About 15k sqft, 2story brick, concrete roof.  It was renovated in the 50s and AC was added.  two huge, watercooled, 460v3ph Chrysler Airtemp units.  When we bought it in 97 it had been vacant for 23 years and the water cooling towers on the roof were beyond saving so it got new air/air air conditioners.  But before removing the old ones, I connected the power and started the compressors with pressure gauges attached.  They ran flawlessly!  Quiet and smooth.  Chrysler built great stuff, even commercial AC.   If the renovation budget had allowed I would have found a way to keep them, but funds were tight so  I took the cheaper route.

Does that mean it just wouldn't slow down,or it would but got rough running?  Big difference in possible causes.
 
If it just won't drop below, it is getting air from somewhere, throttle blades or elsewhere.

I made up a temporary shaft years ago when I swapped a Mustang V6 with C4 into my little Dodge D50.  Intended to use it to test drive and debug, then get a real shaft made by a real shop.  Worked so well, I never got around to the better one.  So my answer is obviously, run it 'til there's a good reason not too.

---All the sample pics and video I saw posted here are describing front brake work.  And, yes, it can be a time saver to remove dust cover, cotter key and nut to pull the wheel/tire and hub as a unit.  No other reason that I know of.   The note about marking the lug and wheel position is to preserve balance in case it was balanced as a unit, common with the old on car balancers.
 
And, the only time I've seen reference to anything similar on the rear is a kluge used by those without the puller.  Loosen the nuts as far as possible and use the tire and wheel assembly as sort of a slide hammer to pull the hub off the axle taper.